The National Institute for Health and Clinical Excellence (NICE) has today (23 March) published its clinical guideline on the diagnosis and management of tuberculosis, and measures for its prevention and control. A partial update of NICE clinical guideline 33 (published in March 2006), the new recommendations focus on the diagnosis of latent TB using interferon-gamma tests (IGT). All the other advice remains largely unchanged from the original guideline.

The guideline addresses which diagnostic strategy is most accurate in diagnosing latent TB in adults and children who are recent arrivals from countries where TB is highly prevalent; in adults and children who have been in close contact with patients with active TB; in adults and children who are immunocompromised; healthcare workers and hard to reach populations.

TB is caused by a bacterium called Mycobacterium tuberculosis ('M. tuberculosis' or 'M.Tb'). It is spread by one person inhaling the bacterium in droplets coughed or sneezed out by someone with infectious tuberculosis. In over 80% of people the immune system kills the bacteria and they are removed from the body. However, in a small number of cases the TB bacteria are not killed and lie dormant (latent TB). Up to 15% of adults with latent TB will go on to develop active TB at some point in their lives and the risk in children may be much higher. In people who are immunocompromised - for example, if they are HIV positive - the chance of developing active TB within five years of infection is up to 50%. Detection of latent TB is therefore important in controlling the disease.

New recommendations for diagnosing latent TB in the guideline include:

To diagnose latent TB in:

Household contacts aged 5 years and older and non-household contacts of all people with active TB:

A Mantoux test should be performed. Those with positive results (or in whom Mantoux testing may be less reliable - for example, people who have had the BCG vaccination) should then be considered for IGT.

If Mantoux testing is inconclusive, refer the person to a TB specialist.

New entrants from high-incidence countries aged 5 - 15 years:

Offer a Mantoux test followed by IGT if positive.

New entrants from high-incidence countries aged 16-34 years:

Offer either IGT alone or a dual strategy. For people aged 35 years or older, consider the individual risks and benefits of likely subsequent treatment before offering testing.

New entrants from high-incidence countries aged under 5 years:

Use Mantoux as the initial test. If positive, taking into account BCG history, refer to a TB specialist to exclude active disease and consider treatment of latent TB.

People who are immunocompromised:

If latent TB is suspected in children and young people who are immunocompromised, refer to a TB specialist.

For people with HIV and CD4 counts (also called T-cells, these are types of cells that help protect the body from infection) of less than 200 cells/mm3, perform an IGT and a concurrent Mantoux test. If either test is positive assess for active TB and consider treating for latent TB.

For people with HIV and CD4 counts of 200-500 cells/mm3, perform an IGT alone or an IGT with concurrent Mantoux test. If either test is positive, assess for active TB and consider treating for latent TB.

Dr Fergus Macbeth, Director of the Centre for Clinical Practice at NICE, said: "Contrary to popular belief TB is not one of those diseases which, like smallpox, has been all but eradicated from our shores. In fact, latest figures show it is on the increase, particularly in our major cities. It is therefore important that the strategies that are used to detect the disease before it has the opportunity to develop into full-blown TB are as robust as possible and based on the best available evidence. When the original guideline was published NICE recommended further research to compare the latent TB diagnostic strategies of conventional skin test only, skin test then interferon gamma test if positive, and interferon gamma test only. Based on a detailed analysis of this further research, the independent Guideline Development Group has concluded that the relative benefit of IGT over the Mantoux test in determining the need for treatment of latent TB infection is not certain - and in the case of younger children it feels that IGT may even perform less well. However, the GDG has made recommendations in populations where they considered IGT to be of clear benefit, especially in cases where IGT would reduce the uncertain diagnosis after Mantoux testing."

NICE has produced a range of tools to help health professionals implement this guideline, including audit support, a costing tool and a slide set, all of which are available on the NICE website.